<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      /* 根标签 可以连续写多个 :root */
      /* :root:root:root {
        color: blue;
      } */
      html {
        color: red;
      }
    </style>
  </head>
  <body></body>
</html>
